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01-12-2012 | Methodology | Uitgave 1/2012 Open Access

Journal of Foot and Ankle Research 1/2012

Visual categorisation of the arch index: a simplified measure of foot posture in older people

Journal of Foot and Ankle Research > Uitgave 1/2012
Hylton B Menz, Mohammad R Fotoohabadi, Elin Wee, Martin J Spink
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Electronic supplementary material

The online version of this article (doi:10.​1186/​1757-1146-5-10) contains supplementary material, which is available to authorized users.

Competing interests

HBM is Editor-in-Chief of Journal of Foot and Ankle Research. It is journal policy that editors are removed from the peer review and editorial decision making processes for papers they have co-authored. The other authors declare that they have no competing interests.

Authors’ contributions

HBM conceived the idea for the study, conducted the statistical analysis and drafted the manuscript. MRF, EW and MJS collected and compiled the data and assisted with interpretation of the data and drafting of the manuscript. All authors read and approved the final manuscript.



Foot posture is considered to be an important component of musculoskeletal assessment in clinical practice and research. However, many measurement approaches are not suitable for routine use as they are time-consuming or require specialised equipment and/or clinical expertise. The objective of this study was therefore to develop and evaluate a simple visual tool for foot posture assessment based on the Arch Index (AI) that could be used in clinical and research settings.


Fully weightbearing footprints from 602 people aged 62 to 96 years were obtained using a carbon paper imprint material, and cut-off AI scores dividing participants into three categories (high, normal and low) were determined using the central limit theorem (i.e. normal = +/− 1 standard deviation from the mean). A visual tool was then created using representative examples for the boundaries of each category. Two examiners were then asked to use the tool to independently grade the footprints of 60 participants (20 for each of the three categories, randomly presented), and then repeat the process two weeks later. Inter- and intra-tester reliability was determined using Spearman’s rho, percentage agreement and weighted kappa statistics. The validity of the examiner’s assessments was evaluated by comparing their categorisations to the actual AI score using Spearman’s rho and analysis of variance (ANOVA), and to the actual AI category using percentage agreement, Spearman’s rho and weighted kappa.


Inter- and intra-tester reliability of the examiners was almost perfect (percentage agreement = 93 to 97%; Spearman’s rho = 0.91 to 0.95, and weighted kappas = 0.85 to 0.93). Examiner’s scores were strongly correlated with actual AI values (Spearman’s rho = 0.91 to 0.94 and significant differences between all categories with ANOVA; p < 0.001) and AI categories (percentage agreement = 95 to 98%; Spearman’s rho = 0.89 to 0.94, and weighted kappas = 0.87 to 0.94). There was a slight tendency for examiners to categorise participants as having higher arches than their AI scores indicated.


Foot posture can be quickly and reliably categorised as high, normal or low in older people using a simplified visual categorisation tool based on the AI.

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